Environmental Engineering Reference
In-Depth Information
The indirect water reuse process (demonstrated in
Figure 2.3
) is a clear
example of combining an artificial water cycle with the natural hydrologic
scheme and involves: (1) surface water withdrawal, processing, and distribu-
tion; (2) wastewater collection, treatment, and disposal back to surface water
by dilution; (3) natural purification in a river; and (4) repetition of this scheme
by communities downstream (Hammer and Hammer, 1996, p. 1).
DID YoU KNoW?
There is the same amount of water on Earth as there was when the
Earth was formed. The water from your faucet could contain mol-
ecules that dinosaurs drank.
Water Supply: The Q and Q Factors
Whereas drinking water practitioners must have a clear and complete under-
standing of the natural and manmade water cycles, they must also factor in
the two major considerations of
quantity
and
quality
, the Q and Q factors.
They are responsible for (1) providing a
quality
potable water supply—one
that is clean, wholesome, and safe to drink; and (2) finding a water supply in
adequate
quantities
to meet the anticipated demand.
Note:
Two central facts important to our discussion of freshwater sup-
plies are that (1) water is very much a local or regional resource, and (2)
problems of its shortage or pollution are equally local problems. Human
activities affect the quantity of water available at a locale at any time
by changing either the total volume that exists there or aspects of qual-
ity that restrict or devalue it for a particular use. Thus, the total human
impact on water supplies is the sum of the separate human impacts on
the various drainage basins and groundwater aquifers. In the global sys-
tem, the central, critical fact about water is the natural variation in its
availability (Meyer, 1996). Simply put, not all lands are watered equally.
To meet the Q and Q requirements of a potential water supply, the drink-
ing water practitioner (whether it be the design engineer, community plan-
ner, plant manager, plant administrator, plant engineer, or other responsible
person in charge) must determine the answers to a number of questions,
such as
1. Does a potable water supply exist nearby that has the capacity for
water to be distributed in sufficient quantity and pressure at all
times?
